Lidar system and method of operation

ABSTRACT

A LIDAR system, preferably including one or more: optical emitters, optical detectors, beam directors, and/or processing modules. A method of LIDAR system operation, preferably including: determining signals, outputting the signals, receiving one or more return signals, and/or analyzing the return signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 63/091,055, filed on 13 Oct. 2020, which is incorporated in itsentirety by this reference.

TECHNICAL FIELD

This invention relates generally to the object detection and/or imagingfield, and more specifically to a new and useful lidar system and methodof operation in the object detection and/or imaging field.

BACKGROUND

Typical lidar systems and methods rely on pulses of light tocharacterize objects in their surroundings. Their performance is oftensignificantly limited (e.g., in terms of range, resolution, accuracy,etc.) due to a need to wait for each light pulse to return beforeemitting the next light pulse. Thus, there is a need in the objectdetection field to create a new and useful lidar system and method ofoperation.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-1B are flowchart representations of an embodiment of the methodand an example of the embodiment, respectively.

FIG. 2A is a schematic representation of an embodiment of the system.

FIG. 2B is a schematic representation of the embodiment of the system inuse.

FIGS. 3A-3B are schematic representations of examples of determiningsignals.

FIGS. 4A-4B are representations of cross-correlation andauto-correlation, respectively, of a first example of a set ofphase-bounded low cross-correlation codes.

FIG. 4C is a representation of cross-correlation of a second example ofa set of phase-bounded low cross-correlation codes.

FIGS. 5A-5B are schematic representations of examples of analyzingreturn signals.

FIGS. 6A-6B are schematic representations of a first and second example,respectively, of applying a matched filter in the time domain.

FIG. 7 is a schematic representation of a specific example of analyzinga return signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments of the inventionis not intended to limit the invention to these preferred embodiments,but rather to enable any person skilled in the art to make and use thisinvention.

1. Overview.

A method 100 of lidar system operation preferably includes: determininga signal S110; outputting the signal S120; receiving a return signalS130; and/or analyzing the return signal S140 (e.g., as shown in FIGS.1A-1B). However, the method 100 can additionally or alternativelyinclude any other suitable elements performed in any suitable manner.The method 100 is preferably performed using a lidar system 200, but canadditionally or alternatively be performed using any other suitablesystem(s).

Many lidar systems and methods characterize distances to objects intheir surroundings based on time delays (e.g., associated with pulses oflight emitted by the systems). In contrast, embodiments of the method100 and/or lidar system 200 described herein use phase delays (e.g., ofencoded light signals, such as periodic signals, emitted by the lidarsystem 200, such as described below in more detail) to characterizedistances to (and/or other information associated with) objects in theirsurroundings. As these phase delays depend on distance (e.g., and areused to characterize a potentially unknown and/or changing arrangementof objects), the encodings used are typically asynchronous. Accordingly,a new type of encoding, consistent with this application, is describedherein.

2. System.

The lidar system 200 preferably includes one or more: optical emitters210; optical detectors 220; beam directors 230; and/or processingmodules 240 (e.g., as shown in FIGS. 2A-2B).

The optical emitter(s) 210 preferably function to (e.g., are operableto) emit one or more optical signals. The optical signals are preferablybeam-like (e.g., laser beams), but can additionally or alternativelyhave any other suitable optical characteristics.

The optical emitters preferably include one or more lasers (e.g., diodelasers). The lasers can include, for example, edge-emitting lasers,surface-emitting lasers (e.g., VCSELs), fiber coupled lasers, and/orlasers of any other suitable types. The lasers are preferably continuouswave lasers (e.g., operable and/or configured to emit substantiallycontinuous wave radiation) but can additionally or alternatively includepulsed lasers (e.g., operable and/or configured to emit pulses ofradiation) and/or any other suitable lasers. In one specific example,one or more of the lasers emit light with a wavelength of substantially900 nm (e.g., 890-910 nm, 875-925 nm, etc.). In a second specificexample, one or more of the lasers emit light with a wavelength ofsubstantially 1550 nm (e.g., 1540-1560 nm, 1525-1575 nm, etc.). In athird specific example, one or more of the lasers emit light with awavelength of substantially 835 nm (e.g., 820-850 nm, 800-870 nm, etc.).The light intensity emitted by the laser is preferably lower than orequal to the limit prescribed by regulatory standards (e.g., the lasercan be compliant with IEC-60825, IEC-62471, etc.), but can alternativelybe higher. The signal power can be within regulatory limits (e.g., lessthan a threshold power, such as 5W 2W, 1W, 500 mW, 200 mW, 100 mW, 50mW, 20 mW, 10 mW, 5 mW, 2 mW, 1 mW, 0.5 mW, 0.2 mW, or 0.1 mW, etc.),preferably less than 1 mW, but can alternatively be higher or lower.However, the lasers can additionally or alternatively include any othersuitable lasers.

Each optical emitter 210 preferably includes one or more modulators.Each modulator is preferably operable to modulate one or more aspects(e.g., phase, intensity, wavelength, etc.) of the light emitted by theemitter. However, the system 200 can additionally or alternativelyinclude any other suitable optical emitters.

The optical detector(s) 220 preferably function to (e.g., are operableto) generate an electrical signal (e.g., current, voltage, etc.) inresponse to optical detection (e.g., representative of the detectedoptical signal), but can additionally or alternatively generate anyother suitable signal (e.g., representative of the detected opticalsignal) in response to optical signal detection. For example, theoptical detectors can include one or more photodiodes (e.g., avalanchephotodiodes). The optical detector(s) 220 can optionally include (and/orbe supplemented by) one or more demodulators (e.g., digitaldemodulators, such as computationally-implemented demodulators; analogdemodulator circuits; etc.), such as demodulators complementary to themodulators (e.g., configured to convert the encoded signal back into theoriginal sequence). However, the system 200 can additionally oralternatively include any other suitable optical detectors.

The beam director(s) 230 preferably functions to direct the opticalsignal(s) between aspects of the system 200 and the externalenvironment. For example, a beam director 230 can direct an emittedoptical signal (e.g., beam) from an optical emitter 210 to an externallocation 30 (within the external environment), wherein the opticalsignal reflects off the external location 30 (and/or other externallocations). The optical signal is preferably reflected back to the beamdirector 230, which directs the reflected signal to an optical detector220. However, the optical signal can additionally or alternatively bereflected to another beam director 230 (e.g., which directs the signalto the optical detector 220), to the optical detector 220, and/or to anyother suitable element(s) of the system 200. Each beam director 230 candirect one or more emitted signal and one or more reflected signals, andcan direct the signals between one or more optical emitters 210,external locations 30, and/or optical detectors 220 (e.g., as shown inFIG. 2B). In one example, the beam director 230 includes one or moremirrors, preferably moving and/or moveable mirrors such as rotatingmirrors (e.g., continuously rotating) and/or MEMS-based mirrors (e.g.,configured to move in response to control inputs), which can direct theoptical signal to many external locations 30 over time (e.g., scanningthe beam over the locations as the mirror rotates). However, the system200 can additionally or alternatively include any other suitable beamdirectors, or include no beam director.

The processing module(s) 240 preferably function to: control otherelements of the system 200, such as the optical emitters 210 (e.g.,controlling optical emission and/or modulation) and/or beam directors230 (e.g., controlling the direction of the beam); receive data fromother elements of the system 200, such as the optical detectors 220(e.g., receiving signals associated with light detection); and/orprocess (e.g., interpret) the received data, such as to determineinformation about the external environment (e.g., positions of theexternal locations 30). The processing module 240 is preferablycommunicatively (e.g. electronically) coupled to the optical emitters210, optical detectors 220, beam directors 230, and/or any othersuitable elements of the system. The processing module 240 preferablyincludes one or more processors (e.g., CPU, GPU, microprocessor, FPGA,ASIC, etc.) and/or storage units (e.g., Flash, RAM, etc.), but canadditionally or alternatively include any other suitable elements. Insome variations, the processing module 240 (and/or a supplementaryprocessing module) can be physically separated from the other elementsof the lidar system (e.g., wherein the lidar system includes acommunication module, such as a wireless communication module,configured to communicate with the processing module). For example, theprocessing module 240 can be a remote computing system (e.g.,Internet-connected server), and the lidar system can communicate withthe remote computing system (e.g., wherein some or all computations ofthe method are performed by the remote computing system). However, thesystem 200 can additionally or alternatively include any other suitableprocessing modules.

In some embodiments, the lidar system 200 includes one or more elementssuch as described in U.S. patent application Ser. No. 16/663,142, filed24 Oct. 2019 and titled “Lidar System and Method of Operation”, and/orin U.S. patent application Ser. No. 16/663,249, filed 24 Oct. 2019 andtitled “Lidar System and Method of Operation”, each of which is hereinincorporated in its entirety by this reference; for example, the lidarsystem 200 can include the entire ‘lidar system 200’ of U.S. patentapplication Ser. No. 16/663,142, the entire ‘lidar system 10’ of U.S.patent application Ser. No. 16/663,249, a subset of one or both, and/orany other suitable combination of elements and/or functionalities of thetwo. However, the system 200 can additionally or alternatively includeany other suitable elements in any suitable arrangement.

3. Encodings.

Signals can be encoded in many different ways. In some embodiments,signal encodings can include low cross-correlation codes (LCCs). TypicalLCCs (e.g., Gold codes, Kasami codes, Hadamard codes, Zadoff-Chusequences, etc.), such as zero cross-correlation codes (ZCCs), may beused in many applications. These codes can exhibit low (e.g., zero)cross-correlation, but only for synchronized applications (e.g.,synchronous CDMA). Phase alignment between the different signals(signals encoded using such encodings) is required in order to achievelow cross-correlation. In contrast, in asynchronous applications (e.g.,in which phase offsets between different signals are unknown,uncontrolled, and/or varying), use of such ZCCs and/or other LCCs willtypically result in cross-correlations no better than (e.g., similar toor worse than) those achieved using pseudo-random noise (e.g., spreadingsequences). For example, the cross-correlation between two ZCCs may bezero for substantially perfect phase alignment (e.g., zero phase offset)but higher (e.g., similar to levels seen with pseudo-random noise) forany non-zero phase offset.

We describe herein a new phase-bounded approach to low cross-correlationencodings. These phase-bounded low cross-correlation codes (PB-LCCs) candefine a phase bound, wherein a set of PB-LCCs exhibit lowcross-correlation across a range of phase alignments within the phasebound (e.g., within a threshold phase shift of zero, such as +/−5, 10,15, 20, 25, 35, 45, 60, 0-10, 10-30, and/or 30-90°, etc., wherein a 360°phase shift correlates with a delay equal to the full period of theencoding) but exhibit higher cross-correlation (e.g., similar to thatexhibited by pseudo-random noise) outside this phase bound (e.g., asshown in FIG. 4A). Additionally, these PB-LCCs preferably also exhibitlow auto-correlation sidelobes (e.g., low auto-correlation for non-zerophase offsets, such as all non-zero phase offsets, non-zero phaseoffsets within the phase bound, non-zero phase offsets within a secondphase bound different from the cross-correlation phase bound, etc.),such as shown by way of example in FIG. 4B.

In some embodiments, one or more sets of PB-LCCs can be determined vianumerical optimization. For example, optimization can be performed usingan objective function based on cross-correlation and/orauto-correlation. The objective function can be based oncross-correlation between encodings within the phase bound. For example,the objective function can be based on (e.g., equal or proportional to)the highest cross-correlation between any two encodings of the setanywhere within the phase bound (this maximum in-bound cross-correlationcan be denoted as C_(max)). The objective function can additionally oralternatively be based on auto-correlation, within the phase boundand/or for any phase offset (e.g., based on the highest auto-correlationanywhere other than a zero phase shift; this maximum in-boundauto-correlation can be denoted as A_(max)). Performing the numericaloptimization can include iteratively modifying one or more encodings ofa set in order to reduce C_(max) and/or A_(max); for example, to reducean objective function based on C_(max) and/or A_(max) (e.g., objectivefunction f=a A_(max)+c C_(max) for any suitable constants a and c,preferably non-negative constants).

A set of PB-LCCs can define by one or more characteristic ratios. Insome examples, the set can define by an in-bound rejection ratioR_(rej)=C_(max)/A₀, wherein A₀ is the minimum zero-phase-offsetautocorrelation. Note that C_(max), rather than a root mean square (orother smoothed representation) of the cross-correlation, is preferablyused for the rejection ratio, as increased values of C_(max) representincreased probability of a single false detection event (which, in someembodiments, is preferably avoided). In some examples (e.g., using 16signals, each with an encoding length of 2048), an analogous overallrejection ratio (e.g., for PB-LCCs, for pseudo-random noise, etc.) mayhave a value typically around 17-20 dB, wherein the overall rejectionratio is defined based on the maximum overall cross-correlation, ratherthan the maximum in-bound cross-correlation. In contrast, within thephase bound, the rejection ratio can be greater (preferably muchgreater) than it is outside the phase bound. For example, the in-boundrejection ratio can be greater than the dynamic range of thesignal-processing hardware (e.g., greater than 30, 40, 50, 60, 70,25-40, 40-60, and/or 60-80 dB, etc.).

The set of encodings can additionally or alternatively define across-bound ratio R_(CB). The cross-bound ratio is preferably defined asthe ratio of the maximum in-band versus out-of-band cross-correlation.In some examples (e.g., for 16 signals, each with an encoding length of2048 and a phase bound of ±3.125%) in which all encodings are normalizedto unity power (e.g., variance), C_(max) may have a value ofapproximately 0.3, whereas the maximum out-of-bound cross-correlationmay have a value of approximately 200, corresponding to a cross-boundratio greater than 600. For examples with a smaller phase bound, a lowervalue of C_(max) may be achievable (e.g., without significant change tothe maximum out-of-bound cross-correlation), resulting in a highercross-bound ratio; whereas a larger phase bound may result in a highervalue of C_(max) and thus a lower cross-bound ratio. In other examples,R_(CB) can be approximately 10, 30, 100, 300, 1000, 3000, 10-100,100-1000, 1000-10,000, and/or any other suitable value.

In some variations, the PB-LCCs can exhibit low cross-correlation withinmost of the phase bound, with the exception of one or more phasealignments (or phase alignment ranges) associated with highercross-correlation. For example, in some such variations, some pairs ofPB-LCCs may exhibit low cross-correlation throughout the entire phasebound, whereas others may exhibit low cross-correlation throughout thephase bound except for a single phase alignment (or small range of phasealignments) at which the cross-correlation is increased (e.g., as shownin FIG. 4C). In a specific example, a set of PB-LCCs can include aplurality of pairs, wherein each such pair of PB-LCCs exhibits lowcross-correlation throughout the entire phase bound, and any othercombination of two PB-LCCs from the set (other than these pairs)exhibits low cross-correlation throughout the phase bound except for asingle phase alignment at which the cross-correlation is increased. Insuch variations, the method can optionally include performingcorrections to compensate for these higher cross-correlation portions(and/or for any other suitable interference arising fromcross-correlation between the codes), such as described below in moredetail regarding S1422.

For variations in which the cross-correlation within the phase boundexhibits one or more small regions (e.g., associated only with a singlephase alignment bin, wherein the bin size is based on the sequencelength of the encodings) of higher cross-correlation values, theobjective function can be based on the highest cross-correlation betweenany two encodings of the set anywhere within the phase bound except forthese one or more small regions of higher cross-correlation. Thismaximum-but-for-small-regions in-bound cross-correlation can be denotedas C_(max) ^(˜). A person of skill in the art will recognize that, whereaspects of C_(max) are described herein, C_(max) ^(˜) may exhibitsimilar properties in such variations having small regions of highercross-correlation. Further, in such variations, for any values based onC_(max) described herein, an analogous value, in which C_(max) ^(˜) issubstituted for C_(max), may be analogously determined and/or applied.

In some variations, each PB-LCC includes multiple sub-sequences (whereineach PB-LCC of a set includes the same number of sub-sequences), whereincross-correlation between the overall PB-LCCs may not be low (e.g., evenwithin the phase bound), but it may be possible to combine (e.g.,mathematically, such as via linear operations) the cross-correlations ofthe sub-sequences to generate a low cross-correlation signal. In oneexample, each PB-LCC includes N sub-sequences, wherein each sub-sequenceof a first PB-LCC corresponds to an associated sub-sequence of one ormore other PB-LCCs of the set (e.g., wherein the correspondingsub-sequences are intended to be output concurrently), and thecross-correlation of the corresponding sub-sequences can be summed (orotherwise combined) to generate a low (or zero) cross-correlationsignal. Each sub-sequence preferably has the same duration, but thesub-sequences can alternatively have any suitable durations. In aspecific example, each PB-LCC of the set includes two sub-sequences(e.g., code 1 includes sub-sequences 1_(A) and 1_(B), code 2 includessub-sequences 2_(A) and 2_(B), etc.). In this specific example, thecross-correlation of any two codes of the set may not be low within anyphase bound; however, a cross-correlation for the first sub-sequences(e.g., cross-correlation of sub-sequences 1_(A) and 2_(A)) can becombined (e.g., summed) with a cross-correlation for the secondsub-sequences (e.g., cross-correlation of sub-sequences 1_(B) and2_(B)), where this combination (e.g., sum) will be low (e.g.,substantially zero) within a phase bound (e.g., throughout the entirephase bound, throughout the entire phase bound except for one or morelimited ranges of larger values, etc.). Accordingly, this property couldbe used to recover responses associated with such PB-LCCs from signalsreceived such as described below regarding the method.

However, the set(s) of PB-LCCs can additionally or alternatively haveany other suitable characteristics and/or can be determined in any othersuitable manner. Further, the signals can additionally or alternativelybe encoded using any other suitable set(s) of encodings.

4. Method.

4.1 Determining a Signal.

Determining a signal S110 preferably functions to determine the signalthat the lidar system outputs, which can function to control variousaspects of object detection performance. Determining the signal S110preferably includes determining a sequence S112 and/or encoding thesequence S113, and can optionally include determining a sequence lengthS111 (e.g., as shown in FIG. 3A). However, S110 can additionally oralternatively include any other suitable elements.

4.1.1 Determining a Sequence Length.

Determining a sequence length S111 can function to control tradeoffsbetween various system performance metrics (e.g., as described below infurther detail). The sequence length is preferably a metric associatedwith sequence size, such as corresponding to a number of substantiallyequal-duration time intervals in which the sequence can take ondifferent values (e.g., different output intensities). In examples, thesequence length can be a number of continuously (or pseudo-continuously)valued output intensities (e.g., represented as digital numericalrepresentations such as integer or floating point representations,represented as analog intensities, etc.) in the sequence, a bit-length(e.g., wherein the sequence is a binary sequence), a number of symbols(e.g., non-binary digits) in the sequence, an effective sequence lengthequal to a signal duration multiplied by a system bandwidth or a valueproportional thereto (e.g., wherein, for a continuously-varying signal,the effective sequence length is representative of the approximatenumber of samples that the system can resolve in the signal), and/or anyother suitable metric associated with sequence size. The same sequencelength is preferably used for multiple sequences, such asconcurrently-emitted sequences (e.g., wherein a plurality of sequencesare output substantially concurrently, such as each output by adifferent optical emitter of the system; example shown in FIG. 3B)and/or serial sequences (e.g., a time series of multiple sequences,emitted by a single optical emitter of the system). Alternatively,different sequence lengths can be used for a single continuous signaland/or multiple, concurrently-emitted signals.

The sequence length is preferably determined as described in U.S. patentapplication Ser. No. 16/663,142, filed 24 Oct. 2019 and titled “LidarSystem and Method of Operation”, which is herein incorporated in itsentirety by this reference (e.g., as described regarding ‘determining asequence length S111’), but can additionally or alternatively bedetermined in any other suitable manner.

In some embodiments, the sequence length is selected to be in the range10-10,000 bits (e.g., between 100 and 5000 bits). However, S111 canadditionally or alternatively include selecting any other suitablesequence length.

The sequence length is preferably determined based on one or moredesired performance metrics (e.g., to achieve at least a minimumperformance level for a first set of metrics, to maximize performanceaccording to a second set of metrics, etc.).

In examples, the sequence length can be automatically determined (e.g.,selected, calculated, etc.) based on operating context, such asgeographic location, system kinematics (e.g., velocity, acceleration),presence of objects detected within a given physical range, performancemetric values, and/or other contextual variables; automaticallydetermined based on a set of target performance metric values (e.g.,received from a user, determined based on operating context); manuallydetermined; and/or otherwise determined. For example, the method caninclude: receiving target values for one or more performance metrics,and selecting the sequence length associated with the receivedperformance metric target values (e.g., from a sequencelength-performance metric value table or other data structure). Theassociation between the performance metric value and the sequence lengthcan be: predetermined (e.g., calculated, tested), iterativelydetermined, and/or otherwise determined. In another example, the methodcan include: adjusting the sequence length until the performance metricssatisfy a set of performance metric target values. However, the sequencelength can additionally or alternatively be determined in any othersuitable manner.

The performance metrics can include accuracy, range, resolution,latency, power consumption, and/or any other suitable metrics (e.g.,used such as described in U.S. patent application Ser. No. 16/663,142,filed 24 Oct. 2019 and titled “Lidar System and Method of Operation”,which is herein incorporated in its entirety by this reference).

Range is preferably the maximum distance at which an object can bereliably detected while implementing the method 200 (e.g., without thepossibility of an aliasing and/or range ambiguity issue, such as arisingfrom periodicity of the output signal; while maintaining the failureprobability below a threshold value, such as less than a 0.1%, 0.2%,0.5%, 1%, 2%, 5%, or 10% complete miss probability, preferably less thana 1% complete miss probability; while receiving sufficiently strongreturn signals to reliably perform the method; etc.). Because the signalperiod typically increases with sequence length (e.g., for a fixedsymbol rate, it increases linearly), range typically increases withlonger sequences (e.g., wherein, to avoid potential periodic rangeambiguity, the range is less than or equal to half the distance that thesignal propagates during one period of the signal, corresponding to theround-trip propagation time of the signal reflecting off a maximum-rangeobject). However, the range may more typically be limited by signalstrength, such as by the strength of the return signals received by thesystem (e.g., wherein return signals reflected from more distant objectsin the environment maybe weaker than those reflected from closerobjects). An increased sequence length can increase the discriminationpower of the matched filter and/or can increase the detectionintegration time, which can enable more reliable detection of moredistant objects (and/or other weakly-returning objects) in theenvironment. In some examples, the sequence length (and/or other signalparameters, such as symbol rate) is selected so that the range (e.g.,ambiguity-limited range, return signal strength-limited range, etc.) ismore than, no less than, and/or substantially equal to a thresholddistance, such as 50, 100, 150, 200, 250, 275, 300, 325, 350, 400, 450,500, 600, 10-50, 50-150, 150-450, or 450-1000 m. In a first specificexample, the threshold distance is 300 m. In a second specific example,the threshold distance is 200 m, limited by return signal strength,which can correspond to a sequence length that would enable anambiguity-limited range of 1-5 km (e.g., approximately 2 km). In avariation of the second specific example, the threshold distance is 500m, limited by return signal strength, which can correspond to a sequencelength that would enable an ambiguity-limited range of 3-10 km (e.g.,approximately 5 km).

Accuracy can include detection failure probability (e.g., “completemiss” probability), detected distance accuracy (e.g., “Cramer-Rao lowerbound” or “CRLB”), and/or any other suitable accuracy metrics. Latencyis preferably the amount of time per sweep (e.g., time betweenconsecutive signal outputs at a particular beam orientation, such ascorresponding to beam outputs at all the probed external locations).Resolution is preferably the angular spacing between adjacent beamdirections (e.g., the angle defined between the vectors from the opticalemitter to each of two adjacent external locations).

However, S110 can alternatively include using a predetermined sequencelength (e.g., rather than determining a sequence length dynamically),and/or the sequence length can be determined in any other suitablemanner.

4.1.2 Determining a Sequence.

Determining a sequence S112 preferably functions to determine one ormore unique sequences (e.g., all having a particular sequence length,such as a sequence length determined in S111). Each sequence can be adigital sequence (e.g., binary sequence, non-binary digital sequence,etc.), an analog (e.g., continuously-valued and/orpseudo-continuously-valued) sequence, such as a sequence of integersand/or of real numbers (e.g., in digital, analog, and/or any othersuitable representation), and/or any other suitable sequence. In someembodiments, the sequences can be determined such as described in U.S.patent application Ser. No. 16/663,142, filed 24 Oct. 2019 and titled“Lidar System and Method of Operation”, which is herein incorporated inits entirety by this reference, but can additionally or alternatively bedetermined in any other suitable manner.

The sequences are preferably determined to achieve a high degree oforthogonality (e.g., orthogonality between different sequences,orthogonality between encoded signals corresponding to the differentsequences, orthogonality to environmental noise, etc.). Accordingly, thesequences are preferably determined to meet one or more of the followingcriteria (e.g., as described in more detail in U.S. patent applicationSer. No. 16/663,142, filed 24 Oct. 2019 and titled “Lidar System andMethod of Operation”, which is herein incorporated in its entirety bythis reference): high auto-correlation at zero time delay (zero phaseoffset); low auto-correlation away from zero time delay (non-zero phaseoffset); and/or low cross-correlation with other signals present in thesystem's environment (e.g., other sequences of a set). The lowcross-correlation can be exhibited for some or all phase offsets (e.g.,for a set of PB-LCCs, exhibited for phase offsets within a phase bounddefined by the set of PB-LCCs; alternatively, exhibited for all phaseoffsets within the phase bound except for one or more small phasealignment ranges for which the PB-LCCs are known to exhibit highercross-correlation, such as described above in more detail regarding‘Encodings’).

S112 can optionally include determining a detection range limit (and acorresponding phase bound) and/or otherwise determining a phase bound.The detection range limit is preferably consistent with (e.g., no morelimiting than) other system limitations (but alternatively can be morelimiting). For example, the detection range limit can be consistent withhardware and/or regulatory considerations (e.g., light intensity,photodetector sensitivity, hardware noise floor, etc.) which limitdetection range to a threshold distance D₁ (e.g., 500 m). In thisexample, the encoding sequence length can correspond to a greaterdistance D₂ (e.g., 5 km), preferably wherein D₂=tc/2, where t is theencoding sequence period and c is the speed of light. Thus, in thisexample, the phase bound can be set greater than or equal to D₁/D₂; forD₁=500 m and D₂=5 km, D₁/D₂=10% of the period, corresponding to a phasebound equal to or wider than +/−36°. The phase bound can bepredetermined (e.g., based on system calibration and/or performancemetrics, based on historical data, based on any other suitableinformation, etc.), dynamically determined (e.g., based on currentand/or recent system performance and/or other data), and/or determinedin any other suitable manner.

Preferably, S112 includes determining multiple sequences (e.g., eachassociated with a different emitter, such as different emitters of thesystem, of different systems, etc.), preferably each having the samesequence length (e.g., a single sequence length determined in S111). Insome embodiments, S112 includes determining a set of PB-LCCs (e.g., asdescribed above in more detail, such as regarding ‘Encodings’). In suchembodiments, S112 preferably includes determining the set of PB-LCCsbased on the phase bound (e.g., phase bound determined such as describedabove), more preferably wherein the set exhibits a phase bound equal to(or wider than) the phase bound determined as described above.

Determining the sequences can include selecting from a plurality ofpredetermined encodings (e.g., selecting based on one or moreparameters, such as sequence length and/or phase bound), dynamicallygenerating (e.g., computing) the encodings (e.g., based on, such as inresponse to determining and/or receiving, one or more parameters, suchas sequence length and/or phase bound), and/or determining the encodingsin any other suitable manner. For example, the system can maintain adatabase of orthogonal sequence sets (e.g., sets of PB-LCC) for each ofa plurality of sequence lengths and/or phase bounds. The database canoptionally include a matched filter set for each orthogonal sequence set(e.g., Fourier transforms and/or discrete Fourier transforms of each ofthe sequences and/or corresponding encoded signals).

However, the sequences can additionally or alternatively be determinedin any other suitable manner.

In examples, the sequences can include one or more of: continuously (orpseudo-continuously) valued output intensities (e.g., represented asdigital numerical representations such as integer or floating pointrepresentations, represented as analog intensities, etc.), binaryoutputs (e.g., high and low, such as on and off, values), symbols (e.g.,corresponding to non-binary digits), continuously-varying outputs,and/or any other suitable sequence elements.

4.1.3 Encoding the Sequence.

Encoding the sequence S113 preferably functions to generate an encodedsignal based on the sequence (e.g., for each sequence determined inS112, generating a corresponding encoded signal). The generated signalis preferably periodic, repeating the encoded sequence, more preferablywherein there is no (or substantially no) temporal gap between sequencerepeats (e.g., wherein the encoded sequence restarts as soon as theprevious iteration ends) but alternatively including substantialtemporal gaps between some or all sequence repeats. However, thegenerated signal can alternatively be aperiodic and/or have any othersuitable characteristics. Generating the encoded signal preferablyincludes modulating a carrier signal (more preferably, a continuous-waveor substantially continuous-wave carrier signal), such as an opticalcarrier (e.g., laser output) of substantially constant amplitude orsubstantially periodically-varying amplitude (e.g., sinusoid, squarewave, etc.). S113 is preferably performed such as described in U.S.patent application Ser. No. 16/663,142, filed 24 Oct. 2019 and titled“Lidar System and Method of Operation”, which is herein incorporated inits entirety by this reference, but can additionally or alternatively beperformed in any other suitable manner.

The sequence can be encoded for use in an amplitude-modulated continuouswave (AMCW) lidar system, a frequency-modulated continuous wave (FMCW)lidar system, and/or any other suitable lidar system. Accordingly,encoding the sequence preferably includes performing amplitudemodulation and/or optical frequency modulation on the carrier signal(e.g., continuous-wave carrier signal). For example, a binary sequencecan be encoded for use in an AMCW system, or an analog (orpseudo-analog) sequence can be encoded for use in an FMCW system. Thesequence can be encoded using a modulation method (or multiple methods),preferably a digital modulation method (e.g., onto a carrier signal suchas a sinusoid). The modulation method is preferably a phase-shift keying(e.g., BPSK, QPSK, 8-PSK, higher order PSK, etc.), but can additionallyor alternatively include quadrature amplitude modulation (QAM), pulseamplitude modulation (PAM), frequency-shift keying (FSK),amplitude-shift keying (ASK), and/or any other suitable modulationmethod. Alternatively, no carrier signal and/or modulation method can beused. In a first such example, S113 includes directly mapping bitsand/or symbols to output intensities. In a first specific example ofthis example, S113 includes mapping 0 bits to a low or substantiallyzero intensity and mapping 1 bits to a high intensity, or vice versa. Ina second specific example of this example, S113 includes mappingsequence values (e.g., integer values, real number values such asfloating-point values, etc.) to corresponding output intensities (e.g.,wherein the sequence values and output intensities, such as outputpowers, define a substantially linear relationship). In a second suchexample, S113 includes directly mapping bits and/or symbols to changesin output intensity, such as mapping 0 bits to an unchanged intensityand mapping 1 bits to a change in intensity (e.g., flip from one levelto the other), or vice versa.

However, the sequence can additionally or alternatively be encoded inany other suitable manner.

4.2 Outputting the Signal.

Outputting the signal S120 preferably functions to emit an output (e.g.,a beam, preferably a beam of light) that includes the signal to beoutput (e.g., the signal determined in S110). S120 can includecontrolling a transducer, preferably an optical emitter such asdescribed above (e.g., a laser), to output the signal. For example, amodulator (e.g., as described above, such as regarding the system 200)can be employed to include the signal in the output, such as bymodulating the amplitude, optical frequency, and/or any other suitablecharacteristic(s) of an optical carrier (e.g., continuous-wave laserbeam) based on the signal. S120 preferably includes continuouslyoutputting the signal (e.g., for a periodic signal), but canalternatively include outputting the signal a single time and/or anyother suitable number of times with any suitable timing. In embodimentsincluding multiple transducers (e.g., multiple optical emitters, such asmultiple lasers), S120 preferably includes emitting multiple outputs,more preferably concurrently or substantially concurrently (e.g.,emitting all the outputs continuously or substantially continuously,emitting pulsed and/or sporadic outputs at substantially the same timeas each other, etc.). However, the multiple outputs can additionally oralternatively be emitted with any other suitable timing.

During S120, the beam director is preferably controlled to direct theoutput signal toward one or more external locations 30 (e.g., asdescribed above, such as regarding the system 200). Upon reaching theexternal location(s), the beam can be reflected (e.g., back toward thesystem). In one example, the beam director can be controlled to directthe beam substantially in a first direction over a first dwell timeinterval (e.g., substantially equal to one period of the signal), thenin a second direction over a second dwell time interval, preferablysubstantially equal in duration to the first dwell time interval, and soon, eventually substantially returning to the first direction andrepeating continuously (e.g., until the output parameters, such assequence length, resolution, symbol rate, etc., are altered).

S120 is preferably performed such as described in U.S. patentapplication Ser. No. 16/663,142, filed 24 Oct. 2019 and titled “LidarSystem and Method of Operation”, which is herein incorporated in itsentirety by this reference, but can additionally or alternatively beperformed in any other suitable manner.

4.3 Receiving a Return Signal.

Receiving a return signal S130 preferably functions to detect one ormore reflections of the output signal (e.g., from one or more objectswithin an environment surrounding the system, such as objects at theexternal location(s)). The signal can be received at a transducer (e.g.,of the system, such as close to and/or otherwise collocated with theoptical emitter or other output transducer of the system), preferably anoptical detector (e.g., photodiode, such as an avalanche photodiode(APD), etc.), such as described above regarding the system 200. In someembodiments (e.g., wherein multiple signals are output substantiallyconcurrently), multiple signals (e.g., reflections of different outputsignals, different reflections of a single output signal, etc.) can bereceived at the transducer during S130 (e.g., received substantiallyconcurrently and/or otherwise temporally overlapping). The return signalis preferably a reflection (e.g., direct reflection, specularreflection, etc.) of the output signal. However, S130 can additionallyor alternatively include receiving any return signal associated with(e.g., induced by) the output signal, and/or receiving any othersuitable signals.

The received signal(s) are preferably sampled (e.g., by a circuit, suchas an analog-to-digital converter circuit, that samples an electricaloutput of the transducer, such as the current and/or voltage generatedby the transducer in response to reception of the received signals) at asufficient rate to resolve the signal(s), such as sampling at a rate atleast twice the bandwidth of the anticipated signal(s). In one example,the received signals are sampled at a rate of at least 2.5 times thesymbol rate of the output signals (e.g., for a 100 MHz symbol rate,corresponding to a 125 MHz output signal bandwidth, sampling at a rateof at least 250 MHz).

S130 is preferably performed such as described in U.S. patentapplication Ser. No. 16/663,142, filed 24 Oct. 2019 and titled “LidarSystem and Method of Operation”, which is herein incorporated in itsentirety by this reference, but can additionally or alternatively beperformed in any other suitable manner.

4.4 Analyzing the Return Signal.

Analyzing the return signal S140 preferably functions to determine theposition of one or more external locations (e.g., off of which thesignal was reflected) relative to the system. Analyzing the returnsignal S140 preferably includes selecting a sample from the returnsignal S141, filtering the sample S142, and/or determining informationbased on the signal S143 (e.g., as shown in FIG. 5A). However, analyzingthe return signal S140 can additionally or alternatively includedetermining additional information S144 and/or any other suitableelements.

Selecting a sample from the return signal S141 preferably functions toselect a portion of the return signal for analysis. The selected sampleis preferably a contiguous window of the received signal. The samplewindow is preferably sufficiently long in duration to capture an entireperiod of the output signal. In one example, the sample duration ispreferably no less than the sum of the signal period (e.g., equal to thesequence length divided by the symbol rate) and the maximum propagationdelay (e.g., equal to twice the range divided by the speed of signalpropagation, such as the speed of light in the environment surroundingthe system, which corresponds to the round-trip propagation time for anoutput signal that reflects off an external location at a distance equalto the range). However, S141 can additionally or alternatively includeselecting a window of any other suitable duration, and/or selecting anyother suitable sample.

Filtering the sample S142 preferably functions to isolate portions ofthe sample associated with (e.g., substantially matching) thecorresponding output signal. S142 preferably includes performing adigital filtering process (e.g., performed computationally), such asimplemented by a processing module (e.g., as described above). However,S142 can additionally or alternatively include otherwise performing thefiltering process (e.g., analog and/or digital filtering process, suchas one implemented by a filter circuit). The filter applied to thesample is preferably a matched filter (or substantially matched filter)for the corresponding output signal, but can additionally oralternatively be any other suitable filter.

In one embodiment, S142 includes determining a convolution S1421 (e.g.,circular convolution) of the output signal with the sample, preferablywherein one of the two are time-reversed (e.g., convolution of atime-reversed version of the periodic output signal with the sample, orconvolution of the periodic output signal with a time-reversed versionof the sample), such as a circular convolution of a time-reversedversion of the periodic output signal with the sample. Althoughdescribed herein as determining a convolution of the sample with theoutput signal, a person of skill in the art will recognize that S142 cananalogously include determining a correlation of the sample and theoutput signal.

In a first variation, the convolution is determined (partially orentirely) in the frequency domain. For example, determining theconvolution can include: determining a Fourier transform (e.g., discreteFourier transform, such as the FFT) of the sample, determining a Fouriertransform (e.g., discrete Fourier transform) of the output signal(and/or retrieving a previously-determined Fourier transform of theoutput signal, such as one determined for a prior iteration of S142),multiplying the transformed output signal with the transformed sample(e.g., determining the Hadamard product of the transformed output signaland the transformed sample), and determining an inverse Fouriertransform (e.g., inverse discrete Fourier transform) of the product(which is the convolution of the two).

In a second variation (e.g., in which the PB-LCC is a binary code), theconvolution is determined in the time domain (e.g., entirely in the timedomain, without transformation into and/or out of the frequency domain).In some examples of this variation, if the PB-LCC is a binary code, thecomputational requirements associated with determining the convolutioncan be significantly reduced (as compared with computation of the PB-LCCfor an analog code and/or a digital code including several levels). Forexample, the computation may include only delay and sum operations,which (in some examples) may be easily implemented in a GPU, FPGA,and/or ASIC and/or require only minimal computational resources toperform.

In one such example, determining the convolution includes determining aset of delay times based on the binary code, generating a set of delayedcopies of the sample based on the set of delay times, and summing thedelayed copies. The set of delay times is preferably determined suchthat it includes one delay time associated with each ‘high’ leveloccurrence (e.g., ‘1’ bit) of the binary code (e.g., such that the setof delay times is collectively indicative of the binary code), whereinthe delay time is preferably equal to the occurrence time of theassociated ‘high’ level occurrence (relative to a reference time, such acode start time); in some cases (e.g., in which the first bit of thecode is a ‘1’), one of the delay times may be 0, corresponding to nodelay. For each delay time, a corresponding delayed copy of the sampleis preferably generated; in the case of a 0 delay time (indicating nodelay), the original sample can be used as one of the delay times of theset, and a person of skill in the art will understand that, under thesecircumstances, the original sample can serve as a “corresponding delayedcopy” even though, in some examples, no delay operation may be performedto generate it. In this example, the convolution is equal to the sum ofthe delayed copies of this set, and so the sum of the delayed copies ofthe set is preferably determined. In a first specific example (e.g., asshown in FIG. 6), the binary code 01010000 would result in a set of twodelay times (corresponding to the two ‘1’ bits): 1 bit duration (whereina ‘bit duration’ is the length of time between subsequent bits in theoutput signal) and 3 bit durations, respectively. Accordingly, in thisspecific example, two delayed copies are preferably generated and summedto determine the convolution: one delayed by (t−1) bit durations, andanother delayed by (t−3) bit durations, where t can be any constantadditional delay (for example, t can be equal to the code duration; oralternatively can be equal to the largest subtrahend of all the delaytimes, such that the corresponding delay time is zero). In a secondspecific example, the binary code 1011010 would result in a set of fourdelay times (corresponding to the four ‘1’ bits): 0 bit durations, 3 bitdurations, 4 bit durations, and 6 bit durations. Accordingly, in thisspecific example, four delayed copies are preferably generated andsummed to determine the convolution: a first delayed by (t−0)=t bitdurations, a second delayed by (t−3) bit durations, a third delayed by(t−4) bit durations, and a fourth delayed by (t−6) bit durations (where,as before, t can be any constant additional delay).

In a variation of this example, delayed copies of a sample that has beentime-reversed could be generated (rather than delayed copies of theoriginal sample), with relative delays equal to the negative of thedelays described above. Following the first specific example above, thebinary code 01010000 would result in delay times of 1 and 3. Optionally,any constant additional delay could be added uniformly to (or subtracteduniformly from) all of the delayed copies, and the matched filter couldbe applied analogously to the description above. In this variation, theresulting filtered sample will typically be time-reversed relative tothe filtered sample produced by the example described above, andpossibly shifted temporally.

However, S1421 can additionally or alternatively include determining theconvolution in any other suitable manner.

S142 can optionally include correcting one or more signals forcross-correlation S1422 between codes (e.g., PB-LCCs), preferably codescorresponding to different concurrently (or substantially concurrently)transmitted optical outputs. The signal(s) to correct is preferably thesample after one or more prior filtering steps, such as application of amatched filter (e.g., as described above regarding S1421), but canadditionally or alternatively include the sample as received and/or anyother suitable signals.

In one example, N different optical outputs are transmitted concurrently(e.g., in S120), each corresponding to a different code (e.g., adifferent PB-LCC), and S1421 is performed on the sample for each of theN codes, resulting in N filtered samples. Each combination of two of theN codes corresponds to a respective cross-correlation, denoted C_(i,j)for the cross-correlation of codes i and j. For any particular filteredsample i (denoted S_(i)) associated with a particular code i (and aparticular optical output i encoded with the code i), the correction canbe performed based on the cross-correlations of that particular codewith the other N−1 codes (e.g., based on portions thereof, such as theportion of each that is within the phase bound defined by the PB-LCCs)and on the other N−1 filtered samples. In one example, correctingfiltered sample 1 (having a peak at t₁, corresponding to a phase shiftof t₁) can include, for each of the other filtered samples S_(j) (eachhaving a peak at corresponding to a phase shift of t_(j)) where j∈{2, .. . , N} (i.e., filtered samples 2 through N): based on the filteredsample S_(j)(t), the associated cross-correlation C_(i,j)(τ), and therelative phase shift Δt_(1,j)=t_(j)−t₁ between them, determining theexpected interference I_(1,j) in filtered sample S₁ that is expected toarise from the optical signal(s) encoded with code j, and subtractingthis interference I_(1,j) from the filtered sample S_(i); in an example,the interference I_(i,j)(t) can be calculated as the product of thephase-shifted filtered sample S_(j)(t−Δt_(i,j)) and the associatedcross-correlation C_(i,j)(Δt_(i,j)) (that is,I_(i,j)(t)=S_(j)(t−Δt_(i,j))C_(i,j)(Δt_(i,j))), but can additionally oralternatively be determined in any other suitable manner. Accordingly,the corrected sample S′₁ can be calculated based on the equationS′₁=S₁−Σ_(j=2) ^(N)I_(1,j). Analogously, for any given value of i∈{1, .. . , N}, and the associated filtered sample S_(i), the corrected sampleS′_(i) can be calculated by subtracting I_(i,j) for each j≠i:S′_(i)=S_(i)−Σ_(j≠i)I_(i,j). In an alternative variation, the correctionmay be performed based only on a subset of the other filtered samples(e.g., and thus, only a subset of the cross-correlations). For example,if the cross-correlation between two codes is low throughout theentirety of a range of interest (e.g., the phase bound defined by twoPB-LCCs), those cross-correlations could be ignored (e.g., treated as ifthey were equal to zero for all phase offsets) for the purposes of thesecorrections, thereby reducing the computational requirements of thecorrection.

S1422 is preferably performed to correct each filtered sample (but canalternatively be performed only for a subset thereof). Each filteredsample is preferably corrected based on the other filtered samples(e.g., without correction, or having undergone the same number ofcorrected iterations as the sample currently being corrected). However,in alternate variations, some or all of the other samples used toperform the correction may have already been corrected (e.g., havingundergone more corrections than the sample currently being corrected),and/or alternatively having undergone fewer corrections than the samplecurrently being corrected (e.g., not having undergone any corrections).In a first example (e.g., performed after correcting filtered sample 1,but before correcting any other filtered samples), filtered sample 2 iscorrected based on a corrected sample 1 and (uncorrected) filteredsamples 3 through N:S′₂(t)=S₂(t)−S′₁(t−Δt_(2,1))C_(1,2)(Δt_(2,1))−Σ_(j=3)^(N)S_(j)(t−Δt_(2,j))C_(2,j)(Δt_(2,j)). In a second example (e.g.,performed after correcting all filtered samples except filtered sampleN), filtered sample N is corrected based on the corrected samples 1through N−1: S′_(N)(t)=S_(N)(t)−Σ_(j=)^(N−1)S′_(j)(t−Δt_(N,j))C_(N,j)(Δt_(N,j)).

In some embodiments, S1422 can be performed multiple times (e.g.,iteratively), such as to determine further corrected samples based onthe corrected samples. For example, each further corrected sample S″_(i)can be determined based on the corrected samples and thecross-correlations asS″_(i)(t)=S′_(i)(t)−Σ_(j≠i)S′_(j)(t−Δt_(i,j))C_(i,j)(Δt_(i,j)), and soon for additional iterations. In a specific example, two iterations ofS1422 are performed, and the further corrected samples S″_(i) are usedas “filtered samples” in the method elements that follow (e.g., thosedescribed below, such as S143 and/or S144).

S142 preferably generates a filtered sample that is a function of delaytime. The filtered sample is typically a discrete function (e.g., thesample and/or output signal includes data only at discrete points intime, the calculation is performed at discrete points in delay time,etc.) but can alternatively be a continuous function and/or any othersuitable function.

S142 can optionally include zero-padding the sample (e.g., wherein oneor more zero-valued points are inserted into the sample, such as betweeneach observed point of the sample determined in S130). The sample can bezero-padded before performing the filtering, and/or the filtered samplecan be zero-padded after filtering.

However, S142 can additionally or alternatively include filtering thesample in any other suitable manner.

Determining information based on the signal S143 preferably functions todetect the presence and/or absence of (and/or to determine information,such as distance, optical properties, etc., regarding) objects in theenvironment (e.g., the external locations off of which the output signalis reflected). S143 is preferably performed based on the filtered samplegenerated in S142 (e.g., the filtered sample generated in S1421, thecorrected or further corrected sample generated in S1422, etc.), but canadditionally or alternatively be performed using the as-received sampleselected in S141 and/or any other suitable information associated withthe signal (e.g., received signal).

S143 can optionally include determining a noise floor of the sample. Thenoise floor can be determined based on the sample selected in S141,based on a calibration sample, preferably collected while the outputsignal is not being emitted (e.g., while no output signals are beingemitted, when all other output signals are being emitted, etc.), basedon any other suitable sample, estimated (e.g., based on typicalconditions), and/or determined in any other suitable manner. The noisefloor can be determined based on (e.g., equal to) a measure (e.g.,median, average, alpha-trimmed average, inter-quartile average, etc.) ofa power spectrum of the sample used to determine the noise floor (e.g.,the sample selected in S141, the calibration sample, etc.).

S143 preferably includes determining a delay time corresponding to anextremum of the data (e.g., a maximum of the sample, preferably thefiltered sample). This delay time is preferably determined using one ormore interpolation techniques (e.g., wherein the determined delay timecorresponds to the maximum-valued interpolated point). Suchinterpolation can have several benefits, including, for example,improving detection accuracy and/or enabling CRLB estimation.

For example, S143 can include determining an interpolated delay time(e.g., corresponding to an extremum of the interpolated data) byperforming a continuous curve interpolation (e.g., parabolicinterpolation, polynomial interpolation such as using a polynomial oforder 2, 3, 4, 5, 6, 7-10 or any other suitable order polynomial, sincfunction interpolation, Taylor-series interpolation, etc.), a discreteFourier transform-based interpolation (e.g., zero-padding a frequencyspectrum associated with a discrete Fourier transform of the data,convolving the zero-padded frequency spectrum with an interpolationkernel such as a sinc function kernel, and generating interpolated timedomain data by determining an inverse discrete Fourier transform of theconvolution), and/or any other suitable interpolation technique(s). Theinterpolation is preferably performed using only (or substantially only)linear computational operations, which can enable rapid computation, butcan additionally or alternatively be performed using any other suitableoperations. The delay time can additionally or alternatively bedetermined using one or more regression techniques (e.g., to determine acontinuous curve, such as a curve of one of the types described aboveregarding interpolation and/or any other suitable type of curve, thatfits the data or a subset thereof, such as a subset near the extremum).

S143 can optionally include applying a delay time correction (e.g.,after interpolation and/or regression). For example, the method caninclude correcting the interpolated delay time based on a correctionrelationship (e.g., predetermined relationship, such as determinedduring a system calibration, fixed for all such systems, etc.) betweenthe interpolated delay time and the corrected delay time, such as arelationship associated with an analytical curve (e.g., polynomial, suchas a polynomial of order 2, 3, 4, 5, 6, 7-10 or any other suitable orderpolynomial) and/or a numerical relationship (e.g., stored in a lookuptable).

In one example, the interpolated delay time is determined by performinga parabolic interpolation using three data points: the extremal datapoint and the point neighboring the extremal data point on either side.In a variation of this example, the interpolated delay time is thencorrected based on a polynomial correction relationship (e.g.,associated with a sixth-order polynomial of the interpolated delaytime).

However, S143 can alternatively include determining the delay timewithout interpolation (e.g., wherein the determined delay time is thetime corresponding to the maximum-valued discretized point of thesample), and/or determining the delay time in any other suitable manner.In embodiments in which a noise floor is determined, if the determineddelay time corresponds to a point exceeding the noise floor (e.g.,greater than the noise floor, a value proportional to the noise floor,greater by more than a threshold amount, etc.; considering a singlepoint, a peak including at least a threshold number of points, etc.),the delay time can be considered to represent a return (e.g., detectionevent), whereas points not exceeding the noise floor are preferably notconsidered to represent returns. If no noise floor is determined, anydelay time determined as described here is preferably considered torepresent a return.

This delay time (e.g., if considered to represent a return) correspondsto the propagation time of the output signal (e.g., time betweenemission from the optical emitter and reception at the opticaldetector). Thus, the delay time typically corresponds to the distance tothe external location from which the beam reflected (e.g., wherein thedelay time is equal to twice the distance divided by the signalpropagation speed, typically the speed of light).

The information determined in S143 (e.g., delay time and/or distancecorresponding to each return) is preferably stored in association withinformation associated with the detected object orientation with respectto the system (e.g., the beam direction). For example, the relativelocation of the object with respect to the system can be stored (e.g.,wherein many such returns result in the determination and/or storage ofa point cloud representing the environment surrounding the system), suchas stored as a point in 3-dimensional space (e.g., wherein the origin ofthe space represents the system). Optionally, other information can bestored in association with this information, such as the correspondingvalue (e.g., of the raw and/or interpolated sample), phase information,and/or any other suitable information.

Additionally or alternatively, S143 can include selecting data fordownstream analysis (e.g., and not include determining a particulardelay time or times). In one embodiment, S143 can include selecting oneor more portions of the sample (e.g., filtered sample) as portions ofinterest. For example, these portions could include the one or moretimes corresponding to (e.g., surrounding by a threshold time window,such as a bit duration) one or more maxima in the sample. In thisexample, these one or more portions of interest (which may correspondapproximately to the delay times that could have been determined asdescribed above) can be provided for downstream analysis (e.g., spatialand/or temporal filtering, such as based on a number of samplescorresponding to different times and/or positions in the environment),in which determinations about these portions (e.g., filtering for truereturns versus noise, determining precise return timing, etc.) can bemade.

However, S143 can additionally or alternatively include determining anyother suitable information in any suitable manner.

S140 can optionally include determining additional information S144. Insome embodiments, S144 can function to detect multiple extrema (e.g.,corresponding to multiple reflections) in a single sample. For example,S144 can enable recognition of “multi-return” events (e.g., wherein abeam is incident on the edge of an object, and thus a first portion ofthe beam is reflected by the object which a second portion of the beamcontinues on, possibly to be reflected by a second object; wherein abeam is incident on a semi-transparent object, and thus the beam ispartially reflected by the object and partially transmitted through theobject, possibly to be reflected by a second object; etc.). Preferably,S144 includes detecting all discernable extrema of interest (e.g.,maxima above the noise floor).

In one embodiment, S144 includes, after performing S143, altering thesample (e.g., filtered sample) to remove the peak that includes thedelay time determined in S143 (e.g., as shown in FIG. 7). In a firstexample, removing the peak includes selecting the peak by finding thenearest local minimum on each side of the determined delay time (whichcorresponds to the maximum), and altering all data between those minima(e.g., setting all values between the minima to zero, linearlyinterpolating between the minima, etc.). In a second example, removingthe peak includes performing a peak-fitting procedure to select the peak(e.g., determining a peak fit function corresponding to the peak), thensubtracting the peak fit values (e.g., values of the peak fit function)from the corresponding points of the sample. In a third example,removing the peak includes approximating a selection of the peak byselecting a window of points (e.g., predetermined number of points,predetermined delay time window, etc.) on each side of the determineddelay time (preferably including the point at the determined delaytime), and altering all data within the window (e.g., setting all valuesbetween the minima to zero, linearly interpolating between the pointsjust outside either side of the window, etc.). However, the peak canadditionally or alternatively be removed (and/or otherwise diminished,marked to be ignored, etc.) in any other suitable manner.

In this embodiment, after removing the peak, S143 is repeated using thealtered sample (e.g., wherein this repetition of S143 can determine asecond delay time, corresponding to the maximum value of the alteredsample). The process of removing peaks and then repeating S143 using thenewly-altered sample is preferably repeated until no additional returnsare found (e.g., all peaks that exceed the noise floor have beenremoved).

In a second embodiment, S144 includes performing a modified version ofS143 in which multiple extrema (e.g., in the filtered sample) and/orassociated delay times are determined substantially concurrently (e.g.,all determined during a single pass through the filtered sample). Inthis embodiment, S144 is preferably performed instead of S143, but canadditionally or alternatively be performed after S143 and/or with anyother suitable timing. In this embodiment, S144 preferably includessearching the filtered sample for local extrema (preferably maxima, butoptionally minima), wherein the first several or top (e.g., largest orsmallest magnitude) several extrema are stored. In an example of thisembodiment, a specific number of buffers are designated for storinginformation associated with the extrema (e.g., delay time, magnitude,etc.). Upon finding an extremum, the associated information is stored inan empty buffer. In a first variation, if no empty buffers remain, andthe search for extrema terminates (e.g., and S144 is complete). In asecond variation, if no empty buffers remain, the magnitude of thecurrent extremum is compared to the least significant (e.g., for maxima,smallest magnitude) stored extremum; if the current extremum is moresignificant, its associated data is stored in the buffer, replacing thepreviously-stored information associated with the less significantextremum.

However, S144 can additionally or alternatively include determining anyother suitable information in any suitable manner.

In embodiments in which multiple signals are output concurrently and/orclose in time (e.g., wherein several such signals may be receivedconcurrently in S130), S140 is preferably performed for each such outputsignal (e.g., as shown in FIG. 5B). For example (e.g., wherein thesequence length and symbol rate for all the signals is equal), a singlesample can be selected (as described above regarding S141) for all suchoutput signals, and then some or all remaining elements of S140 (e.g.,S142, S143, S144, etc.) can be performed (e.g., independently) for eachsuch output signal, using the same sample. Because the different outputsignals preferably have high mutual orthogonality (e.g., as describedabove, such as a set of PB-LCCs having high mutual orthogonality withina phase bound), a high degree of discrimination between the differentoutput signals can be enabled by this method (e.g., wherein most noiseassociated with the other output signals is filtered out in S142).Embodiments of the method can additionally or alternatively achieve highmutual interference immunity (e.g., immunity to interference from noiseoriginating from other sources, such as from other lidar systems and/orany other suitable emitters), especially for longer sequence lengths, asthese noise sources will also typically have reasonable highorthogonality to the output signals used by the lidar system.

In some examples, S140 is performed such as described in U.S. patentapplication Ser. No. 16/663,142, filed 24 Oct. 2019 and titled “LidarSystem and Method of Operation”, which is herein incorporated in itsentirety by this reference, and/or one or more elements of S140 areperformed such as described in U.S. patent application Ser. No.16/663,142 regarding (e.g., wherein one or more other elements of S140are performed such as described above). However, S140 can additionallyor alternatively be performed in any other suitable manner.

4.5 Repeating Elements of the Method.

The method 100 can optionally include repeating one or more of theelements described above. One embodiment includes performing S120 and/orS130 (e.g., continuously performing S120 and S130, preferablysubstantially concurrently), preferably while repeating S140 and/orchanging the beam direction (e.g., sweeping the beam around theenvironment, such as described above). In this embodiment, all orsubstantially all of the signal received in S130 is preferably analyzedover the iterations of S140 (e.g., wherein for each iteration of S140, adifferent sample of the received signal, preferably the sampleimmediately following the previous sample, is used).

In a variation of this embodiment, some or all elements of S110 canoptionally be repeated (e.g., periodically, such as after a thresholdperiod of time, a threshold number of iterations of S140, a thresholdnumber of sweeps of the beam, etc.; sporadically; in response totriggers; etc.), wherein S120, S130, and/or S140 can continue to beperformed (e.g., based on the new sequence(s) determined in the mostrecent iteration of S110). In a first example of this variation, a newsequence length is selected (e.g., to alter some or all of theperformance metrics, such as accuracy, range, resolution, latency,etc.), such as described above regarding S111, after which S112 isperformed based on the new sequence length. In a second example, a newsequence (or sequences) is selected (e.g., as described above regardingS112) using the same sequence length as before (e.g., with a differentphase bound). This second example can optionally be performed if thesequence orthogonality (e.g., to external noise sources, such as noisefrom other lidar systems) is suspected to be poor (e.g., if signaldiscrimination performance is poor). For example, if another nearbylidar system (e.g., mounted to a vehicle operating near the presentlidar system) is using one or more output signals similar to (e.g., notsufficiently orthogonal to) one or more of the current output signals ofthe present lidar system, the method may not achieve sufficient immunityto this interference source. Thus, by changing the sequence(s), greatermutual interference immunity may be achieved. In a variation, the secondexample can additionally or alternatively be performed if the phasebound is smaller than desired (e.g., causing an undesired rangelimitation) and/or if the phase bound is larger than desired (e.g.,resulting in a low rejection ratio, such as wherein a high-intensityreturn signal cannot be sufficiently filtered out of a lower-intensityreturn signal, resulting in potential false detection events). Thissecond example can additionally or alternatively be performedperiodically, sporadically, and/or with any other suitable timing (e.g.,changing operation to diagnose whether the system is operating asdesired), and/or performed for any other suitable reason.

However, the method 100 can additionally or alternatively includerepeating any other suitable elements with any suitable timing.

Although omitted for conciseness, the preferred embodiments includeevery combination and permutation of the various system components andthe various method processes. Furthermore, various processes of thepreferred method can be embodied and/or implemented at least in part asa machine configured to receive a computer-readable medium storingcomputer-readable instructions. The instructions are preferably executedby computer-executable components preferably integrated with the system.The computer-readable medium can be stored on any suitable computerreadable media such as RAMs, ROMs, flash memory, EEPROMs, opticaldevices (CD or DVD), hard drives, floppy drives, or any suitable device.The computer-executable component is preferably a general or applicationspecific processing subsystem, but any suitable dedicated hardwaredevice or hardware/firmware combination device can additionally oralternatively execute the instructions.

The FIGURES illustrate the architecture, functionality and operation ofpossible implementations of systems, methods and computer programproducts according to preferred embodiments, example configurations, andvariations thereof. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, step, or portion of code,which comprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block can occurout of the order noted in the FIGURES. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

We claim:
 1. A method for environment mapping, comprising: selecting aset of phase-bounded low cross-correlation codes (PB-LCCs), the set ofPB-LCCs comprising a first PB-LCC and a second PB-LCC, wherein the setof PB-LCCs defines a phase bound; generating a first optical outputrepresentative of a first output signal, comprising modulating a firstsubstantially continuous-wave carrier signal based on the first PB-LCC;generating a second optical output representative of a second outputsignal, comprising modulating a second substantially continuous-wavecarrier signal based on the second PB-LCC; throughout a time period,concurrently transmitting the first and second optical outputs into anenvironment; at an optical sensor, receiving a return signal, the returnsignal comprising: a first reflection, from a first object within theenvironment, of the first optical output; and a second reflection, froma second object within the environment, of the second optical output;determining a sample by selecting a contiguous time window of the returnsignal; generating a first filtered sample, comprising filtering thesample based on the first PB-LCC; determining a first phase delayassociated with the first filtered sample, wherein the first phase delayis within the phase bound; based on the first phase delay, determining arelative location of the first object; generating a second filteredsample, comprising filtering the sample based on the second PB-LCC;determining a second delay time associated with the second filteredsample; and based on the second delay time, determining a relativelocation of the second object.
 2. The method of claim 1, furthercomprising: generating a third optical output representative of a thirdoutput signal, comprising modulating a third substantiallycontinuous-wave carrier signal based on a third PB-LCC of the set ofPB-LCCs; throughout the time period, concurrent with transmitting thefirst and second optical outputs into the environment, transmitting thethird optical output into the environment; generating a third filteredsample, comprising filtering the sample based on the third PB-LCC;determining a third delay time associated with the third filteredsample; and based on the third delay time, determining a relativelocation of a third object within the environment; wherein the returnsignal further comprises a third reflection, from the third object, ofthe third optical output.
 3. The method of claim 2, further comprising:generating a fourth optical output representative of a fourth outputsignal, comprising modulating a fourth substantially continuous-wavecarrier signal based on a fourth PB-LCC of the set of PB-LCCs;throughout the time period, concurrent with transmitting the first,second, and third optical outputs into the environment, transmitting thefourth optical output into the environment; generating a fourth filteredsample, comprising filtering the sample based on the fourth PB-LCC;determining a fourth delay time associated with the fourth filteredsample; and based on the fourth delay time, determining a relativelocation of a fourth object within the environment; wherein the returnsignal further comprises a fourth reflection, from the fourth object, ofthe fourth optical output.
 4. The method of claim 3, wherein the set ofPB-LCCs defines a set of pairwise cross-correlations, the method furthercomprising: based on the set of pairwise cross-correlations and thesecond, third, and fourth filtered samples, correcting the firstfiltered sample for interference associated with the second, third, andfourth reflections; based on the set of pairwise cross-correlations andthe first, third, and fourth filtered samples, correcting the secondfiltered sample for interference associated with the first, third, andfourth reflections; based on the set of pairwise cross-correlations andthe first, second, and fourth filtered samples, correcting the thirdfiltered sample for interference associated with the first, second, andfourth reflections; and based on the set of pairwise cross-correlationsand the first, second, and third filtered samples, correcting the fourthfiltered sample for interference associated with the first, second, andthird reflections.
 5. The method of claim 1, wherein the first andsecond PB-LCCs define a cross-correlation, the method furthercomprising: based on the cross-correlation and the second filteredsample, correcting the first filtered sample for interference associatedwith the second reflection; and based on the cross-correlation and thefirst filtered sample, correcting the second filtered sample forinterference associated with the first reflection.
 6. The method ofclaim 5, further comprising: based on the cross-correlation and thecorrected second filtered sample, further correcting the corrected firstfiltered sample for interference associated with the second reflection;and based on the cross-correlation and the corrected first filteredsample, further correcting the corrected second filtered sample forinterference associated with the first reflection.
 7. The method ofclaim 1, wherein filtering the sample based on the first PB-LCCcomprises applying a matched filter, associated with the first PB-LCC,to the sample.
 8. The method of claim 7, wherein applying the matchedfilter is performed in the frequency domain.
 9. The method of claim 7,wherein: the first PB-LCC is a binary code; and applying the matchedfilter is performed in the time domain.
 10. The method of claim 9,wherein applying the matched filter to a signal comprises: generating aset of delayed copies of the signal based on a set of delay times,comprising, for each delay time of the set of delay times, generating,based on the delay time, a respective delayed copy of the set of delayedcopies, wherein the set of delay times is indicative of the firstPB-LCC; and determining a sum of the delayed copies of the set. 11.method of claim 1, wherein the first optical output is substantiallyperiodic and the second optical output is substantially periodic. 12.The method of claim 11, wherein: concurrently transmitting the first andsecond optical outputs into the environment comprises transmitting thefirst and second optical outputs substantially continuously throughoutthe time period; and the return signal is received at the optical sensorduring the time period.
 13. The method of claim 1, wherein modulatingthe first substantially continuous-wave carrier signal based on thefirst PB-LCC comprises performing optical frequency modulation.
 14. Themethod of claim 1, wherein modulating the first substantiallycontinuous-wave carrier signal based on the first PB-LCC comprisesperforming amplitude modulation.
 15. The method of claim 1, whereindetermining the first phase delay comprises: determining an extremum ofthe first filtered sample; and determining the phase delay based on theextremum.
 16. The method of claim 1, wherein: the first optical outputis transmit into the environment by a first laser; and the secondoptical output is transmit into the environment by a second laser. 17.The method of claim 16, wherein the optical sensor comprises aphotodiode, wherein receiving the return signal comprises receiving thefirst and second reflections concurrently at the photodiode.
 18. Themethod of claim 1, wherein: the first optical output is transmit intothe environment in a first direction; and the second optical output istransmit into the environment in a second direction different from thefirst direction.
 19. The method of claim 1, further comprising, beforeselecting the set of PB-LCCs, selecting a sequence length, wherein thelength of each PB-LCC of the set is equal to the sequence length. 20.The method of claim 19, wherein the sequence length is selected based ona first set of desired performance metrics comprising at least one of:accuracy, range, resolution, or latency, the method further comprising:based on the return signal, selecting a second sequence length differentfrom the sequence length; selecting a second set of PB-LCCs, the secondset of PB-LCCs comprising a third PB-LCC and a fourth PB-LCC, whereinthe length of each PB-LCC of the second set is equal to the secondsequence length; generating a third optical output representative of athird output signal, comprising modulating a third substantiallycontinuous-wave carrier signal based on the third PB-LCC; generating afourth optical output representative of a fourth output signal,comprising modulating a fourth substantially continuous-wave carriersignal based on the fourth PB-LCC; throughout a second time period afterthe time period, concurrently transmitting the third and fourth opticaloutputs into an environment; at the optical sensor, receiving a secondreturn signal, the second return signal comprising a reflection of atleast one of the first or second optical output; determining a secondsample by selecting a contiguous time window of the second returnsignal; generating a third filtered sample, comprising filtering thesecond sample based on the third PB-LCC; and generating a fourthfiltered sample, comprising filtering the second sample based on thefourth PB-LCC.
 21. The method of claim 1, wherein: the first PB-LCCcomprises a first sub-sequence and a second sub-sequence; the sample isselected from a first portion of the return signal associated with thefirst sub-sequence; and filtering the sample based on the first PB-LCCcomprises: determining a second sample by selecting a second contiguoustime window from a second portion of the return signal, the secondportion associated with the second sub-sequence; combining the first andsecond samples to generate a combined sample; and applying a matchedfilter, associated with the first PB-LCC, to the combined sample.